1. Field of the Invention
The present invention generally relates to a printing apparatus, and relates particularly to a printing apparatus suitable for systems, such as point-of-sale (POS) terminals and electronic cash registers (ECR), used in processing monetary transactions.
2. Description of the Background Art
In system having a host processor or computer supplying image, character and/or control data to a printer to produce an output, it is often necessary that the host computer inquire as to the various states of the printer. For example, the host may inquire as to whether there is any paper in a paper supply mechanism, whether there is sufficient toner or ink, whether there is a paper jam or any other malfunction. In response to any of these states, the processor may control the flow of data to the printer or merely notify the user of the malfunction. This can be accomplished by including a status request command within the control command set, and sending the printing apparatus status data to the host computer by executing the status request command when it is received from the host. As a result, the host computer sends the status request command as required to obtain the current status of the printing apparatus.
However, when the status of the printing apparatus changes between one execution of the status request command and the next execution of the status request command, the host computer is not informed the instant such change occurs, and a slight time lag may occur. To reduce the delay time to status change detection, the host computer frequently sends the status request command to the printing apparatus at a very short interval. This frequent sending of the status request commands greatly increases the processing performed by the host computer.
In addition, because the host computer does not know which of the printing apparatus statuses has changed, it is necessary to receive all status data with each output of the status request command, thus increasing the amount of status data and the processing overhead required to interpret the received status data. Furthermore, this large volume of status data is sent from the printing apparatus even when there is no change in the printing apparatus status, significantly reducing the efficiency of status data interpretation because status data having the same content is received and interpreted more than once consecutively. Finally, frequent execution of the status request command by the printing apparatus also reduces the throughput of the printing operation.